Variable Frequency Drives

methods to control the stator and rotor flux angles

What else does a Flux Vector Control VFD use?

VFD voltages into shaft

High carrier frequency from the ______________ can induce ________________ into the ________________ of the motor

standard motor winding insulation.

High voltages spikes from a VFD can damage what?

often by microprocessors like the type used in computers.

How are VFD's controled?

converts DC from the dc link filter to AC for the load

Inverter

Shaft encoders

Inverter Duty motors can have what installed on them at a later date?

IGBT

Rectifier may also have _________ _________ _________ _____________

a special rectifier section in the VFD

Regenerative Braking requires what?

18 pulse

The _______- pulse rectifier is good at reducing problem harmonics, but is more expensive

Special cables

Due to the nature of the electrical output of a VFD __________ __________ may be needed when connecting a VFD to a motor

deceleration

Dynamic braking offers braking for ___________________

to prevent build up of induced voltage between the shaft and bearing

Explain the below feature of an Inverter Duty Motor: shaft bonding rings

Voided warranty and cause damage

For all installation issues. refer to the manufacturer's installation manual. Failure to do so May result in what?

compatible

For any motor and VFD combination, it is critical that the motor and VFD are

Proportional Integral Derivative control

PID

PID

Proportional Integral Derivative Control

microprocessor

what does the control circuit consist of?

Closed-Loop

A VFD is used to control a pump motor, if the pump is required to maintain a specific pressure under any condition of use, which VFD control would be the best choice?

direct

Closed loop VFD Speed control uses __________________ feedback from the motor to tell the VFD its exact speed and shaft position

False

Using pulse width modulation the output frequency of the inverter is reduced if the number of pulses generated per cycle is also reduced True or False

is the most common and lowest cost configuration of the three techniques.

V/Hz PWM control techniques

Electrical noise and is defined as a sinusoidal component of periodic wave having a frequency that is an integral multiple of the fundamental frequency.

What is Harmonic distortion best described as?

Variable Frequency AC power frequency

The _____________ _________________ drive uses an _____(AC,DC) power supply(single phase or three phase) and converts it to a 3 phase output at a selected __________________.

True, Each has their own way of telling the inverter how to create and control the output voltage

Both the microprocessor in the control logic board and the method of programming produce the required output may be different between manufacturers. True or False

Total harmonic distortion

THD

-the input AC voltage. 1) Vpeak=Vrms x 1.141 or Vpeak = Vrms/.707 2)Calculate the rectifier output Vdc = Vpeak x .955 example: (480/707)x.955 =648 Vdc

The output from the 6 pulse bridge rectifier can be calculated based on what? Each diode conducts when it is forward biased and allows the full positive alternation to pass. what is the calculation

inverter

The output section of the VFD is the what?

Pulse width Modulation (PWM)

The process of the Microprocessor telling the IGBT what to do is called what?

the amount of controller output until the sensor measurement matches the set-point

I controls what? the amount of controller output until the sensor measurement matches the set-point

Regenerative Braking

Line Regenerative Braking is also called what?

usually accomplished by keypad settings or locally or remotely by a potentiometer connected to the VFD. or input from a programmable logic controller, or a binary coded decimal signal from a thumb wheel or sensors monitoring process variables.

Manual speed control of a motor is:

A)Fans B)Pumps

Name two types of equipment that can achieve cost saving benefits by being operated by a motor connected to a VFD

Permanent magnet motors, wound field brush-less excited synch motors reluctance motors

Non induction motors that can be used with specific types of VFDs are:

is at minimum a Class 1 wiring method and the control panels to switches, pilot devices and analog signals are self-powered.

One of the factors that is Important when installing a VFD is Control Wiring- Please Elaborate

Voltages induced into the case and shaft of the motor can cause arcing in the bearings of a motor and result in premature bearing failure.

One of the factors that is Important when installing a VFD is Bonding

an incoming ac power supply with a fixed frequency and turns into a pulsating DC

VFD rectifies what?

a fixed bridge rectifier

what is a rectifier most commonly?

Vdc=Vpeak =480/.707 =678 Vdc

what is the maximum voltage of a 480 V VFD?

dynamic braking

what type of braking uses a resistor to dissapate the regenerative voltage as heat

two delta wye

A 12 pulse rectifier uses the output of a transformer with__________ secondary windings. one secondary is ________ (delta, wye)connected, the other is connected __________ (the same, wye, delta). to provide the 30 degree

voltage

Capacitors oppose a change in what?

to prevent build-up of induced voltage between the shaft and bearing

why are bonding rings sometimes installed on the motor shafts ?

460/60=7.67 ratio 60/2= 30 30 x 7.67 =230 Answer is 230.1 Volts

A 460 V, 60 Hz motor is operated by a VFD, If the motor speed is reduced to 50% of the name plate value, what is the required voltage

0-60

A VFD can be programed to deliver an output between ___-____ Hz or higher, depending upon the limitations of the motor and drive

rectifier

A fixed bridge rectifier is commonly used for what? a) inverter, b) rectifier

a keypad

A programmer enters values into the program using what?

Totally enclosed fan cooled

TEFC

Dynamic braking, line regenerative braking Dc injection braking

What 3 types of motor braking is there from a VFD

high temperatures and humidity

What are cooling towers sized for?

Fans Pumps industry Phase conversion

What are some applications of a VFD

Inverter ready Inverter duty vector duty

What are three ratings of induction motors used for VFD Use

Permanent magnet motors Wound field synchronous motors reluctance motors

What are three types of non induction motors suitable for VFD use?

Harmonics distort the voltage and current waveforms.

What do Harmonics do.

IGBT

What is the most common semi conductor switching device to produce PWM Output?

10-40 degrees Celsius

What is the temp operating range for a VFD

575/60 V/Hz

What is the volts per Hz ratio for a 575 V motor with a 60 Hz frequency rating?

closed loop

What kind of control does a system have if a heater is energized by a contactor controlled by a thermostat?

6 pulse, 12 pulse 18 pulse

What kind of pulse can a rectifier be.

Power wiring and control wiring

What wiring should never be run together?

dissipates Waste

Dynamic braking ____________ the energy as _________ heat.

Insulated gate bipolar transistors

IGBT

DC Injection braking

Injecting a dc voltage onto the motor stator windings, producing a steady flux is what type of braking?

Frequency

When controlling the speed of an ac motor, what factors does a VFD change to achieve different speeds

capacitors and/or reactors to

what does the filtering section contain to smooth the DC voltage.

to store the dc voltage and to filter out any surges or transients on the line power coming into the VFD

what is the function of the dc link?

480/.707 = 678.92 x .955 =648.37

6 pulse rectifier is used in a VFD. What is the DC average output voltage if this rectifier has 480 Vac Input?

PID, Proportional Intergral derivative control

Accurate closed loop control is provided by _________________ ________________ ________________ settings in some VFD control logics?

False, most days the cooling requirements never reach full load , and full horsepower capability of the motor is not required.

Most days cooling requirements of a cooling tower reach full load True or False

False they are required to be marked for VFD use.

Motors operated with a VFD are not required to be marked for VFD use. True or False

induction motors non induction motors

Motors that can be used with VFD's may be of what two kind?

it is filtered to a smooth dc voltage

Once a AC voltage is rectified what happens?

False, once the pulsating DC reaches the DC link, it is filtered to provide a steady state dc voltage

Once the pulsating DC reaches the DC Link, it is not filtered and does not provide a steady state dc voltage True or False

VFD's operate best between 10 degrees-40 degrees Celsius. should be in a relatively dust free location and must not be mounted in the following conditions: directly in sunlight, hazardous or corrosive locations high vibration areas

One of the factors that is Important when installing a VFD is Location: please elaborate

Line voltage to the drive input should not vary more than +/- 10%. - greater variation causes most drives to trip. Voltage stability, Install control signal cables independently of eachother and separate from any power wiring- to avoid inducing more electrical noise electrical noise can produce erratic drive behavior that is difficult to troubleshoot

One of the factors that is Important when installing a VFD is Supply Line Power Quality, please elaborate

does not have feedback from the system about its status

Open loop

the controller output to stop the change and bring it back to a steady state

P changes what?

carefully

PID settings have to be ______________ tuned to achieve the desired effect without overshooting, then undershooting in a hunting or oscillating pattern

not induction motors, no voltage is induced in the rotor they do not have a squirrel cage rotor that carries the current to create the necessary rotor magnet fields.

Permanent are only meant for operation with a VFD. These are:

permanent synchronous stator

Permanent magnet rotor , the magnet fields are from _________________ magnets on the rotor and operate with no slip of the rotor to the rotating magnet field of the stator. they can be thought of as a ________________________ motor which requires virtually no speed difference between the rotor and the rotating magnetic field of the ______________ to start the motor

true

Permanent magnet rotor motors may be though as a synchronous motor which requires virtually no speed difference (slip) between the rotor and the rotating magnetic field of the stator in order to start the motor True or False

are only meant for operation with a VFD

Permanent magnet rotor motors:

True

Regeneration may occur in elevators where the motor is used to break an elevators descent from upper floors. True or False

True

Regenerative braking recycles the energy True or False?

this motor has no squirrel cage, no permanent magnets and no wound field winding's. It operates on the principle of magnetic reluctance

Reluctance Motor

error.

The difference between the measured value of the process variable sensor and the set point in the controller is called the __________.

circulating currents rotor core

The high frequencies can also cause __________ currents in the _____________ core causing overheating

V/Hz Flux Vector

The most common PWM output techniques that provide effective motor control are:

Inverter or Vector Magnetizing

The motor is marked as _______________ or ______________ duty rated with the marked allowable speed range of the motor. In addition, they be marked with no-load or _______________ current or other information that may be important when programming the VFD

a magnetic pulse generator an optical encorder

Sensors can be

SCR

Some VFDs use a controlled _________ rectifier to aid soft starts and reduce inrush currents, due to the capacitor charging. but operates like a fixed bridge while running

VFD operation, Minimum speed rated speed to minimum

Some motors may be approved for ________ operation, but only to a ______________________ (Minimum,Maximum) speed as specified for that motor. This may be represented by a ration of ________________ speed to ____________________speed

THD Total harmonic distoration

Supply utility companies specify the _______________ that they allow back into their supply lines

True

The rectifier may also have a IGBT to offer regenerative breaking energy recover. True or False?

puts an electrical load on the motor when it is regenerating or acting like a generator. this causes the motor to slow down

The resistor of Dynamic braking does what?

pulses pulses

To change the frequency to the motor, the number of ___________ and the width of the ________ are either increased or decreased for each half cycle

squirrel cage induction or Synchronous motors

VFD's control the speed of _________________ _________ induction or ___________________________ motors

True.

VFD's must be properly bonded to ground. Effective bonding paths are important in VFD operator motor installations. True or False?

high frequency solid state switching in the drive

VFDs produce Harmonic distortion as a result of:

Vector type

Vector Duty motors are used with _______________ type VFDs for closed loop operation

changing the frequency by adjusting the VFD for the desired speed, input from a PLC program to the VFD or by feedback sensors from monitoring a process

What is done by the operator to control the speed of the motor?

Dynamic braking resistor

What is often included in a DC link to help dissipate the energy from dc voltage regenerated by a motor decelerating of overhauling.

Inverter duty

Which induction motor rated for VFD use provides the greatest operation speed ratio for constant torque loads?

2 pole

Which squirrel cage induction motor will run fastest when connected to a 60 hz supply. 2 pole, 4 pole, 6 pole,8 pole

DC injection braking

Which type of motor braking is employed at a low rotor speeds?

to protect the motor

Why are Harmonic filters used on the Load side of the VFD

to prevent the build-up of induced voltage between the shaft and bearings.

Why are bonding rings installed on the shafts of some motors that are operated by a VFD?

To avoid any issues, you want stability and ensure you calculated for the appropriate voltage drops for long runs.

Why do you want to select to consider voltage stability when installing a VFD?

It requires no feedback from the motor and offers basic drive adjustments

does V/Hz require feedback from the motor?

Induced voltages

Arcing across the bearings in a motor operated by a VFD is most likely caused from

open loop and closed loop

Basic types of control are

VFD

Capacitors oppose a change in voltage, and the expected dc value on the dc link rises to and stays close to peak voltage value for a __________ that is not under load

adds a factor to the calculation to determine a rate or how quickly the controler brings the process variable back to the set-point

D controls what?

final stopping

DC injection braking is used for the __________________

sometimes it may require one, to learn more about the motor it is operating.

Do Flux Vector control Drives require an auto tune?

Yes, they are more complex to program and usually require most of the name plate data on the motor

Do Flux vector controls' need most of the nameplate date on the motor to be entered into the drive?

connecting the motor to a resistor to dissipate the energy as heat

Dynamic braking

is often included in the DC link section to dissipate the energy from dc voltage regenerated by a motor decelerating or overhauling.

Dynamic braking resistor in regards of the dc link

the current through the resistor is controlled by a transistor.

Dynamic braking, to control the amount of braking, what needs to be done?

control

Electrical noise from power wiring ________ control wiring signals

to provide cooling (TEBC) totally enclosed blower cooled)

Explain the below feature of an Inverter Duty Motor: separately fed blower motor

End

Feedback from a closed loop VFD is provided on the _________ of the shaft.

an Improvement over the Basic V/Hz design. the core of this type of control is still V/Hz. also uses methods to control the stator and rotor flux angles to optimize motor control

Flux Vector control is what?

Independently adjusted to produce optimum torque from maximum speed, down to and including zero speed. These components are control the flux vector

Flux vector control logic does what with the motor current (out of phase producing component) and torque (in phase producing component) ?

mathematical algorithms in control software programs to: -adjust the frequency and magnitude of the voltage as in basic V/Hz - Control the phase angle of the voltage and current applied to a three phase induction motor

Flux vector technology is a control scheme that uses:

3% Any distortion above that requires remedial action.

Generally, a limit of ______% THD is allowed

Positive or negative switching of the dc voltage generates an alternating voltage to the motor

How do you generate an alternating voltage from a dc voltage?

the Positive voltage is removed

How do you turn the IGBT off?

based on how effectively the system was set up initially

How effective is a Open loop control on doing its job?

Regenerative energy proced b the motor is dissipated as waste heat by the resistor Heat sinks and fans dissipate the hat

How is heat dissipated in a dynamic braking system?

by switching an IGBT connected to the negative rail of the rectified dc voltage from the dc link.

How is the negative half of the sine wave generated by the IGBT?

semiconductor -emitter, -gate, -collector

IGBT is a _____________ consisting of 3 things what are they

False They can switch on and off several thousand times per second and are very reliable.

IGBT's can not switch on and off several thousand times per second and are not very reliable True or False

400 500

IGBT's can turn on in less than ________ nanoseconds and turn off in less than ___________ nanoseconds

it provides a constant torque produced by the motor although the speed changes

If the V/Hz is to maintain control, the current remains relatively as the motor speed is controlled up and down. what does this provide?

No, Dynamic braking may not work as required

If the motor speed is low, is dynamic braking required?

Full Flux vector Drive. .01%

In a closed loop, the feedback allows the drive, typically a ________ _________ _______________ _________ , to control the percent speed regulation to approx _______% from no load to full load conditions

feedback from the back emfs, stator fluxes and an encoder on the motor shaft that reports rotor position and speed to the drive.

In an closed loop operation the flux drive gets what?

feedback from the motor using the back emfs and stator fluxes

In an open loop operation the flux drive gets what?

the bearings can become pitted and may premeturely wear out.

Induced high voltages from a VFD can cause what in the bearings?

inverter ready inverter duty vector duty rated

Induction motors for use with VFD's may be

inductor

Input line of reactor A large __________in series with the drive on the line side . Inductors oppose change in current and suppress harmonic frequencies before they reach the supply line.

IGBT

Insulated Gate bipolar transistors

are specifically designed for VFD operation

Inverter duty Motors :

Motors have better insulation and thermal capacity standard motors.

Inverter ready motors have:

it tells the IGBT when to turn on how long to stay on when turn off how long to stay off

what does a microprocessor do in regards of a IGBT"?

Field oriented control

what else is Flux vector Technology sometimes called?

Full wave three phase rectifier, 60 degrees out of phase 360/6=60 degrees

what is a 6 pulse?

an inductor and a capacitor the inductor is in series with the output the capacitor is in parallel with the output

what is the DC link section made up of? are they in series or parallel, answer for each device

IGBT - insulated gate bipolar transistor

what is the most common switching device used to provide the high switching speed that is required for PWM inverter operation ?

line regenerative braking

what type of braking recycles the energy produced by decelerating motor back to the electrical system

the control logic circuit

where does the IGBT receive its gate pulse from?

Yes, it can produce higher voltage spikes than the voltage of the supply system.

Can VFD outputs produce voltage spikes higher than the peak of the supply line voltage of the system?

in the rotor core that reduce the otherwise increased iron losses produced by the high carrier frequency

Explain the below feature of an Inverter Duty Motor: Thinner steel laminations:

True

Manufacturers recommend the maximum cable lengths and type of cable True or False

Yes, atmospheres at higher elevations are thinner and more cooling effort is required

Must altitude must be considered where a VFD is to be installed?

Location, supply line power quality Bonding Control wiring

To correctly install VFD, you must pay attention to important factors what are they?

the frequency of the three phase stator currents

To provide a continuous range of synchronous speeds, a VFD drive varies what?

Oil wells Large mining trucks Forestry the pulp and paper industries steel mills

VFD's are used extensively to control the operation of motors in various applications and industries such as:

10 -40 degrees Celsius

VFD's operate best between __________ - ________ degrees Celsius

False, they should not be installed in direct sunlight

VFD's should be installed in Direct Sunlight True or False?

inverter motors

Vector Duty Motor are like _____________ motors

False, they are like Inverter Duty Motors

Vector Duty Motors are like inverter ready motors, but they come complete with shaft encoders that give feedback to the drive about rotor speed and position. True or False

A local operating keypad other control devices connected to a terminal strip through a network where the vd is controlled by a computer or PLC at a location a great distance from the drive

What are three control modes available to the User on a VFD

Harmonic filter techniques are often used on both the load side of the VFD to protect the motor, and on the line side

What can be used to reduce Harmonics?

A motor operating with a VFD runs slower and is subject to voltages higher than the peak of the line and at varying frequencies... which can cause problems for standard 3 phase induction motors

What can cause problems for standard three phase induction motors?

destructive conditions to the Motors insulation, such as pitting. The Result is motor failure,

What can high voltage spikes at the motor's terminal produce?

Produce peak voltage spikes and flow back into the Utility supply lines.

What do the harmonic frequencies do when they combine with the fundamental frequency.

The supply frequency and the number of pools, both of which determine synchronous speed: nsynch=(120xfrequency)/Number of poles Insert PICTURE HERE

What does the Speed of on induction motor depend upon?

Overheating of the motor

What is the major concern if a standard motor is operated by a VFD at slow speeds?

Inverter Duty

What motor is specifically designed for VFD operation?

motors that operate loads that require changes in speed or for loads that vary by amount.

What motors may benefit from a VFD?

to prtect the Utility's supply equipment

Why are Harmonic Filters used on the line side

The fan of a TEFC (Totally enclosed fan cooled) motor.

What cools the motor motor at rated speed?

to withstand voltage spikes

Explain the below feature of an Inverter Duty Motor: Better winding insulation

on the non drive end in addition to the shaft bonding ring to prevent circulating currents

Explain the below feature of an Inverter Duty Motor: insulated bearings

the use of equipment that draws current from the line in a non linear manner

Harmonic distortion results from what?

Are frequencies that are superimposed on a power system as a result of non linear electronic loads such as VFDs

Harmonics

by operating a load at no greater speed than what is required by the load.

How are Energy savings achieved?

Input line reactor

If the THD is too high, __________ on the line side of the VFD can be accomplished with an _____________ ______ ___________

VFD's

______ are sensitive to harmonic distortion and can also be a source of harmonic distortion

Load reactors

___________ __________ can be used between the drive and the motor to help the reduce with reflected wave.

because harmonics can distort the voltage and current wave forms Extra heat in distribution transformers Torque losses in motors, Disruptive noise in communication systems

Can Harmonics cause problems?

a low impedance path for stray currents

What does the Bonding provide?

Changes AC to DC

What does the Rectifier do?

the frequency of the output voltage of the VFD

What does this section control with control logics?

Flux Vector

Which VFD control technique may require an autotune?

V/Hz VFD

Which VFD controls technique reflects the least amount of harmonics back into the power source?

Vdc=Vpeak

The maximum voltage on a dc link is calculated how?

Impedance

The cable run between the motor and drive is seen as ___________ to the VFD

False, it does not necessarily require a three phase input. Most accept a single phase input and can recreate a three phase output

A VFD does only need 3 phase input

induction

A VFD enables an _______________ motor to run at any speed within range of speeds from near standstill to the maximum running speed

PID P I D

A _________ controller can be tuned by adjusting the amounts of the ______ the _______ the _________ has on the algorithms of the control software to achieve ideal control .

VFD Lower

A ______________ on air handling unitis can supply the optimum amoun of air (cool or hot) to meet daily requirements. Operating a fan at _______________(Lower,Higher) speeds requires less power

Yes

A flux vector VFD with open loop control is used to control a SCIM. If the motor load increases and greater motor slip results, could this VFD automatically adjust the voltage, independently from the frequency, to increase the motor torque and speed? No or Yes?

True

A flux vector control has more exact speed control under changing load conditions True or False

False it usually requires more information to function as a true flux vector drive. the number of parameters can be in the 100's.

A flux vector drive usually requires less information than a V/Hz to operate

True

A motor may have a 4:1 rated ration when operating constant torques loads, but a 20:1 ratio when operating variable torque load. Some motors are approved at rations of 1000:1 for very slow speeds. True or False

1/4 (a Quarter of )

A motor with an operation speed ratio of 4:1 may successfully operated at a minimum of __________ the rated speed of the motor

False

A pulse width Modulation VFD produces a true sinusoidal voltage True or False?

open-loop

A simple V/Hz control of the VFD can be used successfully for _________-______________control with the frequency of the VFD output set. and the motor runs accordingly

40

A standard V/Hz may have up to _____ parameters to enter into its program

True

An Induction motor always runs at a speed slightly less than synchronous speed, do to slip. True or False

A large inductor in series with the drive on the line side . Inductors oppose change in current and suppress harmonic frequencies before they reach the supply line.

An input line reactor is what?

Conductor insulation thickness Conductor Length

Cable inductance and capacitance are directly proportional to which two factors?

Inductance and capacitance Thickness

Cables contain significant values of ___________ and __________ that are directly proportional to the length of cable and the insulation __________ and type

Low

Cabling must provide a _________ impedance bonding path

has feedback from its system about its status , it has direct input from sensors that lets the system adjust for changing conditions.

Closed loop

has direct input from sensors that lets the system adjust for changing conditions.

Closed loop control

a Magnetic field, because it likes to concentrate in ferromagnetic material that is more permeable, rather than air.

Magnetic reluctance is the effect created by:

captures the energy produced by a decelerating motor and sends it back to the electrical system supplying the VFD.

Line regenerative braking,

VFD

Process operations at manufacturing plants or in refinery operations often used elaborate control valves and actuators to control the flow of process fluids within their operations. These systems were maintenance intensive and costly. Using ________, the operator need only to speed up or slow down the AC motor on his pump. This reduces the maintenance costs, reduces energy costs and increases equipment life expectancy.

IGBT IGBT IGBT

Pulse width modulation the ___________ is switched on for a short period of time to only allow a small amount of current to the motor and is then switched off. The _______ is switched on and left on for progressively longer lengths of time until the current in the motor reaches a peak. then the _________ is switched on for progressively shorter lengths of time. decreasing the current to the motor

False, The drive may not be suitable for all motors, and the motor may not be suitable for the use with all types of drives. Consult the VFD manufacturer and the Motor manufacture to ensure compatibility. Follow the manufacture or engineer recommendations for cabling types and installation locations.

The Drive may not be suitable for all motors, but the motor be suitable for all types of drives. True or False

True

The VFD with an open loop runs at a speed according to a set point or parameter programmed into the VFD by an operator either locally or remotely True or False?

Filtered AC

The _____________ DC voltage is then changed by an inverter to ________ at the desired frequency and magnitude under the direction of the control logic.

the required precision of the control for the system nature of the load cost versus benefit.

The type of control system chosen is determined by what?

Open

There is no feedback from the motor as to how much the slip is increasing or decreasing with changing load. What type of control loop is this?

Motor speed control

VFD are used for

Rated motor voltage Rated motor current rated Hz, max and min Hz rated Speed, Max and Min operational speeds Acceleration/deceleration rates Voltage boost local/remote operation dc braking requirements

VFD parameters

fractional thousands 120/208 600

VFD's are available in sizes from ___________________ horsepower to ______________________ of horsepower and accepts voltages from ___________/________ to _________ and higher

harmonics

What is a major undesirable issue associated with operating a VFD for the power system?

External fuses Circuit breakers contactors input isolation transformers output transformers line or load reactor or other active or passive harmonic filtering devices

What are some Auxiliary components

energy savings reduced noise reduced maintenance and cost control flexibility

What are some advantages of VFDs

torque limiting, voltage boost at low speed minimum and max speed control adjustable acceleration and deceleration rates

What are some basic drive adjustments which are offered by the V/Hz PWM control technique?

it is precise speed regulation and torque control

What are some benefits of Flux vector control?

Harmonics Special cabling requirements

What are some disadvantages of VFD's

thinner steel laminations better winding insulation shaft bonding rings insulated bearings or non conductive ceramic bearings separately fed blower motor

What are some features that an Inverter Duty Motor has:

values can be called parameters, macros Modes

What are some other names of the Values that are entered by the programmer for the PWM

Certain speed at peak line voltage of a specific frequency

What are standard 3 phase induction motors designed to operate at?

120Hz (2nd harmonic) 180 Hz (3rd harmonic) 300Hz(5th harmonic)

What are the harmonic frequencies associated with 60hz are what?

Rectifier Dc Link Inverter

What are the three main components or sections of a VFD

V/Hz control technique Flux vector control technique

What are two most common control techniques for producing a PWM output of a VFD

closed loop

What basic type of control requires feedback?

High voltages spikes at the motor's terminals

What can reflected waves can cause what?

motor current (out of phase producing component) and torque (in phase producing component) ?

What components control the flux vector

control logic that controls the switching of the IGBT in the inverter section for a full range of output frequencies

What does a micro processor provide?

PWM Pulse width modulation

What does an inverter use to convert dc to ac?

equalizes voltage differences between non-current carrying motor parts and non-current carrying parts of the wiring system.

What does proper bonding do?

wants to get rid of this error and makes adjustments to have the sensed value and the setpoint value the same.

What does the controller want to do the error(The difference between the measured value of the process variable sensor and the set point in the controller)?

little voltage (regenerative energy) is produced by the motor and little braking power is produced.

What happens at low rotor speeds?

the current rises to excessive values

What happens if the voltage is not reduces as the frequency is reduced?

it is changed by an inverter to AC at the desired frequency and magnitude under the direction of the control logic

What happens to the filtered DC voltage?

Some VFD can Judge how fast the motor is turning from the parameters that are programmed into the VFD. Sensor less flux vector control. FYI(Some open loop sensorless flux vector controlled VFD's can keep track of the speed of the motor to 1% of synchronous speed no matter how the load changes)

What happens when you need more exact control than can be offered with a simple V/Hz open loop control?

two Full wave three phase rectifiers is 30 degrees out of phase 360 degrees/12= 30 degrees

What is a 12 Pulse

3 full wave rectifiers. their supply voltages are 20 degrees out of phase. 360/18=20 degrees

What is a 18 pulse

V/Hz example: 460V/60 Hz = 7.61 V/Hz ratio for some clarification If you wanted the motor to run at 10%, you should supply 10 % frequency. 60Hz x 10%=6 Hz to achieve 6 Hz you'll need to apply a certain amount of voltage which you find by using the ratio that you calculated earlier 6 Hz x 7.61 (Ratio) = 45.66 Volts you will want to apply 45.66 volts to maintain the proper V/Hz ratio. refer to page 23 for more clarification if this shit is just more confusing

What is the Ratio calculation for V/Hz

480/60 = 8

What is the V/Hz ratio for a 480 V, 60 Hz Motor?

They synchronous speed increases Nsync = (120 x Hz)/Poles

What is the effect on synchronous speed if the VFD output frequency, increases above the rated nameplate frequency?

nsynch=(120xfrequency)/Number of poles Insert PICTURE HERE

What is the formula for synchronous speed

60 x 4 = 240

What is the fourth harmonic of a 60 hz system?

60 hz x 7=420 hz

What is the frequency of the 7th Harmonic on a 60 Hz system?

It must be able to invert the excess dc bus voltage to ac voltage at the supply frequency in order to regenerate back onto the system

What must the Special rectifier do? in regards of a Regenerative braking system

inverter section

What section of a VFD converts a dc bus voltage to pulse width modulated output?

Rectifier section

What section of the VD converts ac supply voltage to a dc voltage for the VFD

Dc link Section

What section of the VFD filters the Pulsating DC to smooth dc

shielded against transient voltages. Shield should only be bonded on one end to allow for draining.

What should the analog signals to and from the drive be

Never connect 120VAC to the control boards on VFD. can cause catastrophic results.

What should you never do with Control wiring or Control Boards?

dc injection braking

What type of braking is done by putting a dc voltage on the motor stator windings

open loop

What type of control does a system have if a heater is energized by a contactor controlled by a stop start station?

the IGBT turns on and current flows between the emitter and the collector.

When a positive voltage is applied to the gate of an IGBT of 15v dc, what happens?

dc link

When the pulsating DC voltage leaves the rectifier section it enters the _______ ________ section

an arc across the bearings

When the voltage exceeds the insulating value of the bearing lubricant what else can happen?

A reflected wave occurs

Whenever cable surge impedance does not match the surge impedance of the Motor what occurs?

control room. to enable an operator to view the status of VFDS.

Where are VFD's often networked to?

Flux Vector

Which VFD control technique controls the phase angle of the voltage and current applied to a three phase induction motor?

because it works well with motors ranging in size from fractional hp to over 1000hp Highly reliable affordable it is affordable reflects the least amount of harmonics available to 208 to 600 v, 3 phase provide output frequencies from 0hz to 400 hz in some units

Why is the V/Hz VFD the most commonly used VFD

Electrical noise it can cause erratic drive behavior that is difficult to troubleshoot

Why should you install control signal cables independently of each other and separate from any power wiring?

fewer of the low number harmonics that cause damage.

With the higher number of pulses what does it result in?

controllable power factor current

Wound field Synchronous motor: The speed of the synchronous motor is now _______________ and the wound field allows the _____________ _____________ to be changed for power factor correction by changing the ____________ flow in the field

Brushless

Wound field synchronous motors with _______________ excitation can also be used with VFD's

3 bonding Radio Frequency Interference.( RFI)

______________ bonding conductors are used in some VFD cables to provide this extra bonding conductor area and help with the reduction of _________ __________ ___________(RFI)

IGBT's this makes the rectifier bi-directional, ac to dc one way (normal operation) and dc to ac the other (Regenerative braking)

_______________ may be incorporated into the bridge rectifier of the VFD to do the required inversion as gated by the control logic for the regenerative braking. What does this make the rectifier?